Neurotransmitter-gated ion channels mediate synaptic transmission throughout the nervous system. The nicotinic acetylcholine receptor (AChR) from skeletal muscle has served as a prototype for understanding the members of the superfamily of receptors, which includes neuronal nicotinic, glycine, GABAA, and 5-HT3 receptors. The essential function of this class of proteins is to transduce neurotransmitter binding into opening of an intrinsic ion channel. To better understand how neurotransmitter-gated ion channels function, the work proposed in this application will identify amino acids in transmembrane domains of the AChR that govern rates of opening and closing of the channel. The approach combines site-directed mutagenesis of residues in transmembrane domains and expression in mammalian cells with single channel recording and kinetic analysis. The overall findings will relate transmembrane domain structure to elementary steps underlying gating of the AChR channel.